Image display devices provided with backlights, such as liquid crystal display devices, can control the luminances of the backlights on the basis of input images, thereby suppressing power consumption by the backlights and improving the quality of display images. In particular, by dividing a screen into a plurality of areas and controlling the luminances of backlight sources corresponding to the areas on the basis of portions of an input image within the areas, it is rendered possible to achieve lower power consumption and higher image quality. Hereinafter, such a method for driving a display panel while controlling the luminances of backlight sources on the basis of input image portions within areas will be referred to as “area-active drive”.
Image display devices of area-active drive type use, for example, LEDs (light emitting diodes) of three colors, i.e., R, G and B, and LEDs of white as backlight sources. Luminances (luminances upon emission) of LEDs corresponding to areas are obtained on the basis of, for example, maximum or mean pixel luminances within the areas, and provided to a backlight driver circuit as LED data. In addition, display data (in the case of a liquid crystal display device, data for controlling the light transmittance of the liquid crystal) is generated on the basis of the LED data and an input image, and the display data is provided to a display panel driver circuit. Note that in the case of a liquid crystal display device, the luminance of each pixel on the screen is the product of the luminance of light from the backlight and the light transmittance based on the display data. The display data is generated on the basis of an input image and a maximum luminance (hereinafter, referred to as a “display luminance”) with which display is provided in areas by all LEDs emitting light.
The display panel driver circuit is driven on the basis of the display data thus generated, and the backlight driver circuit is driven on the basis of the LED data, so that image display based on the input image is provided.
Note that in relevance to this invention, the following prior art documents are known. Japanese Laid-Open Patent Publication Nos. 2004-184937, 2005-258403, and 2007-34251 disclose inventions of display devices in which the screen is divided into a plurality of areas and the emission luminance of a backlight provided for each area is controlled to achieve a reduction in power consumption. In particular, in the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication No. 2004-184937, backlight sources in non-display regions are automatically stopped from being lit up, thereby achieving a reduction in power consumption.